Clamp compositor's top controls shown ratio on commit from main thread.

cc/trees/layer_tree_impl.cc

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/trees/layer_tree_impl.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 704 matching lines @@
 
 void LayerTreeImpl::set_top_controls_height(float top_controls_height) {
   if (top_controls_height_ == top_controls_height)
     return;
 
   top_controls_height_ = top_controls_height;
   if (IsActiveTree())
     layer_tree_host_impl_->UpdateViewportContainerSizes();
 }
 
-bool LayerTreeImpl::SetCurrentTopControlsShownRatio(float ratio) {
+bool LayerTreeImpl::ClampTopControlsShownRatio() {
+  float ratio = top_controls_shown_ratio_->Current(true);
   ratio = std::max(ratio, 0.f);
   ratio = std::min(ratio, 1.f);
   return top_controls_shown_ratio_->SetCurrent(ratio);
 }
 
+bool LayerTreeImpl::SetCurrentTopControlsShownRatio(float ratio) {
+  bool changed = top_controls_shown_ratio_->SetCurrent(ratio);
+  changed |= ClampTopControlsShownRatio();
+  return changed;
+}
+
 void LayerTreeImpl::PushTopControlsFromMainThread(
     float top_controls_shown_ratio) {
   PushTopControls(&top_controls_shown_ratio);
 }
 
 void LayerTreeImpl::PushTopControls(const float* top_controls_shown_ratio) {
   DCHECK(top_controls_shown_ratio || IsActiveTree());
 
   if (top_controls_shown_ratio) {
     DCHECK(!IsActiveTree() || !layer_tree_host_impl_->pending_tree());
     top_controls_shown_ratio_->PushFromMainThread(*top_controls_shown_ratio);
   }
   if (IsActiveTree()) {
-    if (top_controls_shown_ratio_->PushPendingToActive())
+    bool changed_active = top_controls_shown_ratio_->PushPendingToActive();
+    changed_active |= ClampTopControlsShownRatio();
+    if (changed_active)
       layer_tree_host_impl_->DidChangeTopControlsPosition();
   }
 }
 
 bool LayerTreeImpl::SetPageScaleFactorLimits(float min_page_scale_factor,
                                              float max_page_scale_factor) {
   if (min_page_scale_factor == min_page_scale_factor_ &&
       max_page_scale_factor == max_page_scale_factor_)
     return false;
 
@@ skipping 1331 matching lines @@
 
 void LayerTreeImpl::ResetAllChangeTracking() {
   layers_that_should_push_properties_.clear();
   // Iterate over all layers, including masks and replicas.
   for (auto& layer : *layers_)
     layer->ResetChangeTracking();
   property_trees_.ResetAllChangeTracking();
 }
 
 }  // namespace cc